This invention relates generally to slot antennas and, more particularly, to slot antennas fabricated on relatively thick dielectric substrates.
Semiconductor infrared detectors are often arranged in focal plane arrays and cryogenically cooled to very low temperatures to provide sensitive detection of infrared radiation for various types of space-based sensor systems. These detectors are usually made as small as possible to not only increase the sensitivity and speed of each detector, but also to increase the sensitivity of the entire array by allowing more detectors to be placed in the array. However, it is difficult to couple infrared radiation directly onto a detector that is smaller than about a wavelength of the radiation. Therefore, a small antenna is often used to couple the incident infrared radiation onto the detector.
Infrared detector arrays are typically fabricated on dielectric substrates, such as silicon or quartz, using integrated-circuit fabrication methods, and the antennas are typically fabricated as thin metal film patterns on the substrates. Several types of antennas are often used, such as bow-tie antennas or slot antennas. However, these types of antennas tend to have low gains and poor radiation patterns. One alternative is to make the dielectric substrate very thin, on the order of .lambda./100, thus preventing large energy losses in the dielectric substrate. However, thin substrates on the order .lambda./100 are very difficult to fabricate for infrared wavelengths. Another alternative is to add a superstrate to the dielectric substrate so that the antenna is entirely inside the dielectric, thus increasing the gain. However, the gap between the superstrate and the substrate must be exceedingly small, on the order of .lambda./100, which is also difficult to fabricate for infrared wavelengths. Accordingly, there has been a need for a high-gain, broadband antenna that is easily fabricated on dielectric substrates. The present invention is directed to this end.